Drill stems for deep-well drill rods from non-magnetizable austenitic manganese-chromium alloy steels



United States Patent 3,112,195 DRILL STEMS FOR DEEP-WELL DRILL RODS FROM NON-MAGNETIZABLE AUSTENITIC MANGANESE-CHROMIUM ALLOY STEELS Herbert Souresny, Ternitz, Austria, assignor to Fa. Schoeller-Bleckmann Stahlwerke Aktiengesellschaft, Vienna, Austria No Drawing. Filed May 31, 1960, Ser. No. 32,594 Claims priority, application Austria June 4, 1959 1 Claim. (Cl. 75-126) In deep-well drilling, so-called drill stems are arranged between the drilling tool and the adjacent drill pipe to stabilize the weight load on the bit head. In this way it is ensured that the core bit or bit head will be forced with adequate pressure against the material to be drilled and that the torque transmitted by the drill rod will be adequately transmitted to the bit head even in large depths. Such drill stems are usually made from heattreated steel, mainly from molybdenum-chromium alloy steels as well as of nickel-chromium low alloy steels. The drill stems being subjected during operation to high stresses, which may arise in various cases in a complex form, which cannot be foreseen, the quality of the manufacture regarding the selection of the material and regarding the processing is of high importance. For this reason, drill stems are continually subjected to checks during manufacture and it is highly decisive how the material which is used responds to all machining operations, mainly to being drilled.

In view of improved deep-well drilling methods involving driling to much larger depths it has recently become necessary to supervise the course of the borehole as closely as possible in order to become aware of any deviations in the drilled well. For this purpose, precision measuring instruments are incorporated in the drill stems to enable a recording of deviations from the intended course of the borehole to be registered at any time. In order to ensure a satisfactory operation of the relatively sensitive measuring instruments, it is essential, however, that the drill stems employed distinguish in that they are non-magnetizable as far as possible in order to avoid a disturbance of the function of the electrical measuring instruments by foreign fields.

It is already known to use Monel-K alloys containing at least 63% nickel, at least 25% copper, up to 5% aluminium, up to 0.20% carbon, up to 5% iron and accompanying elements as material for the manufacture of such non-magnetic drill stems. Drill stems of these Monel-K alloys have proved entirely non-magnetic in use and have also the necessary mechanical characteristics, particularly a high yield point, and can be economically machined, particularly as regards the drilling of the drill stems.

In this connection it is apparently significant that the relatively expensive Monel-K alloys have been used in the manufacture of drill stems because in addition to their reliable antimagnetic behavior these alloys ensure the required strength values as well as an extremely high dimensional stability when they are drilled to form the hole in the drill stem. .In view of the considerable depths to which average oil field boreholes are drilled, care is taken to avoid any risk regarding the drill stems because any defects in the same would necessarily require a removal of the entire string of drill rod.

Whereas austenitic alloys steels are also non-magnetizable and it has been known for a long time to improve the lower strength of such steels, particularly regarding the yield point, by cold working or bya precipitation hardening treatment, if desired, it has not been proposed before to use such austenitic steels for drill stems. The previous failure to consider austenitic alloy steels as materials for making drill stems appears to be mainly due to the fact that it has not been possible before to provide steel compositions which in addition to being reliably non-magnetizable and having a high strength have also the essential machinability and, particularly, can be economically machined by drilling to form the hole in drill stems of considerable length after cold working.

The invention provides a method of manufacturing drill stems for deep-well drill rods from non-magnetizable austenitic manganese-chromium steels, in which manganese-chromium steels containing up to 0.35% carbon, up to about 1% silicon, 12-25% manganese, 1020% chromium, up to about 5% nickel, up to about 1% molybdenum and 0.0-50.50% nitrogen, balance iron with the usual accompanying elements, are cold-worked to raise the yield point to kg./ sq. mm. and higher at least adjacent to the ends. These steels may desirably have the additions usual in such alloy steels, such as up to 1.5% tungsten, up to 1% titanium, up to 2% columbiumand/or tantalum, up to 0.5% boron, up to 1.5% vanadium, up to 3% copper and up to 5% cobalt, individually or jointly, in a total amount not exceeding 10%. In this connection, steels, containing up to 0.12% carbon, up to 0.60% silicon, 17-19% manganese, 11.50-l3% chromium, 1.52% nickel, GAO-0.60% molybdenum, 0.100.15% nitrogen, balance iron with the usual accompanying elements, have proved particularly suitable.

In the use of the austenitic steels proposed according to the invention it has surprisingly been found that they can be machined, particularly by drilling to form the hole, in spite of their relatively high strength with the dimensional accuracy required particularly for drill stems and that the bores of the drill stems having lengths up to about 10 metres are entirely satisfactory. It is known that the drilling of the drill stems involves great difii culties and that a high precision of the machine tools is required. Deviations of the bore from the center of the stem may result in dangerous reductions in wall thickness and must be absolutely avoided. This aspect is of essential significance in the evaluation of the machinability (drillability). The strength values of the nonmagnetic alloy steels proposed according to the invention as material for drill stems are virtually similar to those of the usual heat-treated magnetic molybdenum-chromium steels when the same are used after being normalized throughout their length and with heat-treated ends.

It is already known to use nitrogen-containing austenitic manganese-chromium steels for purposes in which the non-magnetic character of these steels is of essential significance. For instance, such steels have been used as stainless shafts, non-magnetic cap rings, binding wires for electric machines, valves for superheated steam, piston rods and similar parts of ships and it has also been proposed to subject these steels to cold working in order to increase their strength. All these previously known fields of application, however, are remote from the use proposed according to the invention, not only regarding a the stresses occurring but also in view of the machining required during manufacture. 'For this reason these suggestions do not provide a hint to use such austenitic manganese-chromium-nitrogen steels as a material for the manufacture of drill stems.

I claim:

A dr-ill stem of nonmagnetic steel alloy for a deep-well drill pipe comprising an alloy steel consisting essentially of 0.01 to 0.25% by weight carbon, 0.10 to 1.00% by weight silicon, 12.00 to 25.00% by weight manganese, 10.00 to 20.00% by weight chromium, 0.05 to 0.50% by weight nitrogen, up to 5.00% by weight nickel, and up to 1.00% by weight molybdenum, the balance being es- 4 sentially iron; said alloy steel being cold worked at least along a portion of the drill stem to a yield point of about 70 kg./mm.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,686 Colwell Apr. 21, 1942 2,334,870 Frank Nov. 23, 1943 2,657,130 Jennings Oct. 27, 1953 2,789,049 De Long et a1. Apr. 16, 1957 2,820,725 Wasserman et a1. Jan. 21, 1958 2,891,858 Regerise et a1. June 23, 1959 

